In order to recover solvents from waste gases or else in order to purify waste gases, condenser coolers or recuperative cold reservoirs are used, through which the solvent flows, a process during which the solvents condense out and freeze out. As soon as sufficient solvent has been separated, the flow of waste gas is guided through another group of condenser coolers. The first group is warmed up, and the solvent can be removed as a liquid product. A device of this type is disclosed, for instance, in German preliminary published application no. DE-OS 34 14 246.
Even though the processes according to the state of the art function satisfactorily, they require elaborate equipment since a double-installation is necessary to freeze out and to thaw the solvents. Furthermore, the mode of alternating operations calls for high energy consumption.